Overridable check valve mechanism



y 6. 1968 J. KOKALY 3,392,633

QVERRIDABLE CHECK VALVE MECHANISM Filed on. 21, 1966 a 49 I8 7/4? flaw I NVENTOR Joseph Kohaly United States Patent 3,392,633 OVERRIDABLE CHECK VALVE MECHANISM Joseph Kokaly, Joliet, Ill., assignor to Caterpillar Tractor Co., Peoria, [1]., a corporation of California Filed Oct. 21, 1966, Ser. No. 588,542

6 Claims. (Cl. 91-469) ABSTRACT OF THE DISCLOSURE A two-way check valve mechanism in the driving fluid supply line to a fluid driven motor normally blocks reversed motion of the motor from external forces applied thereto but yields to provide for the reversed motor motion in the presence of an unusually large counterforce on the motor.

This invention relates to fluid system components and more specifically to a check valve mechanism which provides for a uni-directional flow at a first range of pres sures and for a flow in either direction at a higher range of pressures. The invention is particularly adapted for blocking reversed motion of a fluid driven motor when a relatively small countertorqu-e is externally applied thereto while providing for reversed motion when the countertorque exceeds a predetermined magnitude.

Fluid pressure operated motors are used to power a variety of devices under conditions where it is desirable to prevent reversed motion of the motor. This may be accomplished in some instances by providing a simple check valve between the motor and the source of driving fluid therefor. However there are other circumstances under which it is desirable that the motor be capable of such reversed movement upon the application of an unusually large external force to the mechanism operated by the motor and this is not compatible with the use of a conventional check valve.

An example of a system in which these conditions obtain is the drive mechanism for the elevator of a self loading earthmoving scraper. Such scrapers. have a load carrying bowl with a cutting edge which guides soil upwardly into the bowl as the scraper moves forward. To assist the movement of soil into the bowl and to retain the load in the bowl at the open forward face, a chain and flight elevator is situated above the cutting edge. The elevator may be driven by a hydraulic motor operated from a remotely situated source of high pressure fluid. Under normal circumstances, it is desirable that the elevator move in one direction inasmuch as reversed motion can result in the loss of material from the bowl. As the weight of the material carried in the bowl applies a downward force to the elevator when it is stopped such loss can easily occur if no reverse motion blocking means is present in the system.

Although the blocking of reversed motion of the elevator as discussed above is desirable under normal conditions, an absolute blocking of such motion creates further problems. Large rocks or other objects can become lodged between one of the elevator flights and the scraper cutting edge and the removal of such obstructions becomes unduly complicated if reversed elevator motion is impossible. Under such circumtsances, removal of the obstruction may only be possible by jacking up the entire elevator assembly. Removal is much more readily accomplished if it is possible to force the elevator in a reverse direction a small distance by prying, jacking, or other means. However this requires that the motor which drives the elevator turn in a reversed direction.

It is possible to provide for forced reversed motion of the elevator and motor by utilizing a vent valve in the system between the check valve and the motor. By

3,392,633 Patented July 16, 1968 opening the vent, fluid may be released from the intake side of the motor allowing the motor to be turned back- Wardly. However such a valve must be operated manually and frequently cannot be located at a position readily accessible to the scraper operator without undesirable structural complications.

The present invention is a simple and compact valve mechanism which may be disposed between a motor and source of high pressure driving fluid to impart the desirable capabilities discussed above to the motor. In particular, the valve provides a two way check valve action which blocks reverse motor motion when the counterforce thereon does not exceed a predetermined limit while providing for such motion upon the application of a larger counterfo'rce to the motor.

Accordingly it is an object of this invention to provide a compact and simple valve mechanism having a check valve action within :a limited range of fluid pressures and providing for a two-way fluid flow at pressure above said range.

It is another object of this invention to provide means for blocking reverse motion of a fluid driven motor under normal conditions while providing for such motion upon the application of a greater than normal external force to the motor.

It is still another object of the invention to provide reverse motion limiting mechanism for the drive system of a fluid motor operated self loading scraper elevator which facilitates the removal of obstructions lodged in said elevator.

The invention, together with further objects and advantages thereof, will best be understood by reference to the following specification in conjunction with the accompanying drawing which is an axial section view of a valve mechanism embodying the invention with the associated fluid driven motor, driving fluid supply, and control elements therefor being shown schematically.

Referring now to the drawing there is shown a rotary hydraulic motor 11 which may be of conventional construction and which may be utilized to operate any of a variety of mechanisms known to the art. Motor 11 may, for example, be operatively coupled to the elevator of a self-loading scraper as hereinbefore discussed. Blocking of reversed motion of motor 11 when the motor is stopped, and in the absence of a very strong counterforce thereon, is provided for in the present invention by a compact and simple valve mechanism 12 connected into the inlet conduit 13 through which high pressure driving fluid is supplied to the motor 11.

To drive the motor, 11, a pump 14 has an intake 16 communicated with a reservoir 17 containing a suitable hydraulic fluid such as oil. The outlet conduit 18 of pump 14 is forked with a first branch 19 being coupled to the motor intake conduit 13 through the check valve mechanism 12. The second branch 21 of the pump outlet 18 provides a return line to reservoir 17 through a motor control valve 22 and return conduit 23. The motor outlet 24 also communicates with conduit 23 to return the driving fluid to reservoir 17 for recirculation by pump 14.

Motor 11 is activated by closing control valve 22 inasmuch as pump 14 then supplies fluid under pressure to the motor intake 13 through check valve mechanism 12. Opening of the control valve 22 stops operation of the motor 11 as the pressurized fluid from pump 14 is then returned directly to reservoir 17 through the control valve and conduit 23 thereby bypassing the motor. A pronounced advantage of this type of drive system is that the pump 14 may be situated remotely from the motor 11 and the control valve 22 may be at still a third location which is convenient to an operator, the interconnections between the several components being very simple in that only conduits are required.

Under normal conditions valve mechanism 12, functions to prevent the movement of fluid from motor 11 back toward reservoir 17 through the motor intake conduit 13 when the motor is stopped. This normally prevents reverse motion such as might occur if an external torque is applied to the motor at such time and no flow blocking mechanism is present in the system. However the check valve mechanism 12 further functions to allow such a reverse flow if the counter torque applied to motor 11 exceeds a predetermined magnitude.

Valve mechanism 12 has a housing 27 with an inlet 26 at one end to which pump outlet conduit branch 21 connects. Motor intake conduit 13 connects with an outlet passage 29 in an end closure 28 at the opposite end of the housing 27. The flow passage through housing 27 has a first section 31 adjacent the outlet 29 and a second shorter section 32 of reduced diameter adjacent the in let 26, with a step 33 defining the transition between the two sections.

To provide the valve action, a piston 34 is disposed coaxially within the larger diameter bore section 31 and is slidable therein in an axial direction. Piston 34 has a base portion 36 with a diameter conforming to that of bore section 31 and has a head portion 37 with a diameter slightly greater than that of the smaller section 32 of the bore. A bevel 38 at the end of piston head 37 seats against step 33 to close the fluid passage through the valve mechanism and a compression spring 39 Within bore section 31 urges the piston toward the closed position. Spring 39 extends into the large diameter portion of a bore 41 in piston 34 and bears against a step 42 therein.

T provide for fluid flow through the piston 34 when the piston head 37 is retracted from step 33 bores 43 communicate the region 44 around the head section of the piston with the interior bore 41 thereof.

The structure of valve mechanism 12 as described to this point constitutes a check valve limiting fluid flow between pump 14 and motor 11 to a single direction. Fluid from pump 14 enters the 'valve housing bore section 32 through conduit 19 and reacts against piston head 37. The resulting force retracts the piston head 37 from step 33 allowing the fluid to flow through region 44 and bores 43 and 41 to the motor intake conduit 13. However fluid attempting to flow in the reverse direction reacts against the opposite side of piston 34 and, together with spring 39, seats the piston head 37 against step 33 thereby blocking fluid flow in the direction of pump 14. As the motor 11 cannot turn in a reverse direction without pumping fluid into intake conduit 13, the above described check valve action prevents reverse turning of the motor by relatively small torque forces which may be applied thereto.

Considering now mechanism which provides for overriding of the check valve action when a countertorque above a specific level is applied to the motor 11, a ball check valve assembly 46 is carried on the head 37 of the piston 34. Check valve assembly 46 has a tubular body 47 one end of which is threaded into a bore 48 in the end of the piston head 37. Valve body 47 projects axially from the piston head 37 and has an axial passage 49 which is of reduced diameter at the end adjacent piston 34, with the stepped portion of the passage forming an annnular seat 51 for a ball valve element 52. A compression spring 53 is disposed coaxially Within the valve body 47 with one end bearing against the ball 52 and the other end abutted against a transverse pin 54. Spring 53 thus urges the ball 52 towards seat 51 at which position the flow passage through the check valve 46 is closed.

During operation of motor 11, the check valve assembly 46 remains closed, and is in effect bypassed by the fluid passage at step 33. However movement of piston head 37 against step 33 to block a reverse flow and lock motor 11 results in a fluid pressure being applied to the ball 52 in a direction tending to open the check valve assembly 46 and the valve mechanism 12 is effective to block reverse motion of the motor only while check valve assembly remains closed. Thus spring 53 is selected to exert a force against ball 52 which holds the ball against seat 51 in the presence of a fluid pressure thereon corresponding to the maximum countertorque which motor 11 is to sustain without yielding and undergoing reversed motion. When a countertorque exceeding this valve is applied to the motor 11 ball 52 lifts from seat 51 against the action of spring 53 allowing fluid to flow towards control valve 22 and reservoir 17. The control valve 22 is open at the time, to stop the flow of driving fluid to motor 11 as hereinbefore described, and thus such fluid may exhaust to the reservoir. Accordingly the motor 11 yields to the high countertorque and undergoes reversed motion.

Pressurized fluid systems of this class usually have an over-pressure relief valve which opens to relieve any undesirably high pressure which may develop in the system. In the present invention such a pressure relief valve 56 may advantageously be connected into the system by an inlet conduit 57 communicated with the region 44 of the valve body 27, the relief valve outlet being communicated with reservoir 17. It will be observed that the relief valve 56 is also capable of opening if sufficient back pressure is developed by reverse motion of motor 11. However, the relief valve 56 is not capable of duplicating the action of the check valve assembly 46 since to properly perform its relief function, it must be set to open at a higher pressure than that which opens the check valve assembly 46. Further, relief valve 56 remains coupled to the system under all conditions whereas, as discussed above, check valve assembly 46 is effectively bypassed at such times as pump 14 is driving motor 11 forwardly in the normal manner.

It will be apparent that many modifications are possible within the scope of the invention and it is not intended to limit the invention except as defined in the following claims.

What is claimed is:

1. In combination with a fluid driven motor having a driving fluid inlet and a source of driving fluid therefor wherein said motor may be subjected to an external force tending to produce reversed motion thereof, a means for blocking said reversed motor motion when said external force is below a predetermined magnitude comprising, a first check valve defining a first uni-directional flow passage from said source to said motor intake, a second check valve defining a second oppositely directed unidirectional flow passage communicated with said motor inlet, and biasing means holding said second check valve closed when the fluid pressure at said motor inlet is below a value corresponding to said predetermined magnitude of external force acting on said motor.

2. Means for blocking reversed motion of a fluid driven motor as defined in claim 1 wherein said second flow passage is of substantially reduced cross section relative to said first flow passage.

3. Means for blocking reversed motion of a fluid driven motor as defined in claim 1 wherein said first and second check valves are contained within a common housing having a single fluid inlet communicated with said source and a single fluid outlet communicated with said motor inlet.

4. Means for blocking reversed motion of a fluid driven motor as defined in claim 1 wherein said first check valve is comprised of a valve housing having said first fluid passage extending therethrough, said first fluid passage having a step therein defining a valve seat, a piston disposed within said first passage within said valve housing and being slidable therein, said piston having a head portion seatable against said valve seat to close said first flow passage, and wherein said second check valve is carried by said piston and moves therewith.

5. Means for blocking reversed motion of a fluid driven motor as defined in claim 4 wherein said first flow passage extends longitudinally within said piston, and wherein said second check valve is comprised of a tubular body transpierced through said head of said piston and having a stepped bore defining said second flow passage and having a movable valve member seatable in said stepped bore to 10 UNITED STATES PATENTS 577,489 2/1897 Mills 60-62 XR 1,994,974 3/1935 Weidmann l37493 XR 2,151,057 3/1939 Suth.

3,153,423 10/1964 Biello et al 137493.5

FOREIGN PATENTS 239,475 2/ 1924 Great Britain.

EDGAR W. GEOGHEGAN, Primary Examiner. 

